There are few, if any, cardiovascular functions in health and disease states which do not involve nervous, endocrine and renal functions in their control or regulation. This overall system, therefore, is a highly complex system of many related variables and parameters. It is recognized that effective new tools (systems analysis and computer technology) have been developed which now permit the health and life sciences to deal with such complex systems. The program objective is to understand the interactions of the nervous, endocrine, and renal system in the control and regulation of the cardiovascular system. Hypertension, as a major abnormality involving alterations in the system, is studied in particular. Since these systems and their functions involve a large number of variables linked together in many complex relationships, it is necessary to utilize computers to evaluate the interactions and the behavior of the system itself. By comparing the behavior of the model with reality it is possible to test and improve our concepts. It is necessary to assemble the known concepts into a "model" and to describe as accurately as possible the functions of each of the parts of the model and manner of interaction about such functions if they are not known and to define and describe more precisely those that are now ill-defined; and to create disturbances within the living, natural system and to measure the responses of as many parts of the system as possible. We then create analagous disturbances in the computer model and monitor the equivalent alterations within the model; in this way we continue to improve the model, i.e., to make it behave like the living body. The investigations are particularly concerned with hypertension as well as with the physiological mechanisms of circulatory function.